高强铝合金厚板FSW长焊缝沿长度与板厚方向组织均匀化调控及服役性能响应

高强铝合金厚板搅拌摩擦焊（FSW）在航空航天领域有着广泛应用需求，搅拌区显著的大梯度温度热循环与不均匀塑性变形，已成为航空航天结构件连接制备发展亟待解决的瓶颈问题。本项目围绕复合形状变摩擦系数搅拌头和分区梯度冷却均匀调控铝合金厚板FSW过程中热力耦合这一关键科学问题，开展接头沿长度与板厚方向组织均匀化调控、服役性能响应研究。基于热力耦合均匀调控FSW长焊缝的成形机理，阐明焊缝沿长度与板厚方向组织结构演变规律、不均匀性形成机理、应力应变演变、退化机理、应力腐蚀和蠕变服役性能响应规律；获得接头沿长度与板厚方向服役性能的内在相关性、应力腐蚀敏感性、蠕变机制及组织性能的均匀化调控机理；揭示热力耦合均匀调控FSW工艺与组织、服役性能的关联机制和对应关系。通过变摩擦系数和分区梯度冷却均匀化热力耦合输入，实现厚板FSW接头均匀化高质量制备，研究结果将为FSW接头增强增韧高可靠制备提供理论依据和技术支撑。

Friction stir welding (FSW) has been widely used to join high-strength aluminum alloy thick plate in the aerospace applications. The significant difference of temperature gradient and uneven plastic deformation in the mechanical stirring zone have become a bottleneck problem that needs to be solved in the development of the connection of aerospace structural parts. This project focuses on the key scientific issues that the thermal-mechanical coupling has been regulated uniformly by the composite shape of variable friction coefficient welding tool and the partition gradient cooling during FSW aluminum alloy thick plates process. In this project, it also conducts research on homogenization regulation of microstructure and service performance response along the length and thickness direction of the joint. Based on the forming mechanism of FSW long welds with homogenization regulation of thermal-mechanical coupling, the systematic study is able to clarify the law of microstructure evolution and the formation mechanism of inhomogeneity, the stress-strain evolution, the degradation mechanism, the response law of stress corrosion and creep service performance along the length and thickness direction. The internal relevance of service performance, the stress corrosion sensitivity, the creep mechanism as well as the mechanism of homogenization regulation of microstructure and properties along the length and thickness direction of plate are obtained to establish the mechanism of interactional relation among microstructure, properties, service performance and homogenization regulation of thermal-mechanical coupling FSW process. An attempt is made to develop the new associated control technology using the varying coefficient of friction and the partition gradient cooling for homogenization regulation of thermal-mechanical coupling during FSW process and to realize the manufacture of homogeneous microstructure and properties along the length and thickness direction of plate. These results will provide supporting technology and fundamental for the high reliability of improved toughness and strength in friction stir welded joints.